Atherosclerosis and its associated coronary heart disease are the leading causes of death in the industrialized world. Risk for development of coronary heart disease has been shown to be strongly correlated with certain plasma lipid levels. Lipids are transported in the blood by lipoproteins.
The general structure of lipoproteins is a core of neutral lipids (triglyceride and cholesterol ester) and an envelop of polar lipids (phospholipids and non esterified cholesterol). There are 3 different classes of plasma lipoproteins with different core lipid content: the low density lipoprotein (LDL) which is cholesteryl ester (CE) rich; high density lipoprotein (HDL) which is also cholesteryl ester (CE) rich; and the very low density lipoprotein (VLDL) which is triglyceride (TG) rich. The different lipoproteins can be separated based on their different flotation density or size.
High LDL-cholesterol (LDL-C) and triglyceride levels are positively correlated, while high levels of HDL-cholesterol (HDL-C) are negatively correlated with the risk for developing cardiovascular diseases.
Plasma lipoprotein metabolism can be described as a flux of cholesterol between liver and the other tissues. The LDL pathway corresponds to the secretion of VLDL from the liver to deliver cholesterol by LDL to tissues. Any alteration in LDL catabolism could lead to uptake of excess cholesterol in the vessel wall forming foam cells and atherosclerosis. The opposite pathway is the mobilization of free cholesterol from peripheral tissues by HDL to deliver cholesterol to the liver to be eventually excreted with bile. In humans a significant part of cholesteryl ester (CE) is transferred from HDL to the VLDL, LDL pathway. This transfer is mediated by a 70,000 dalton plasma glycoprotein, the cholesteryl ester transfer protein (CETP).
Mutations in the CETP gene associated with CETP deficiency are characterized by high HDL-cholesterol levels (>60 mg/dL) and reduced cardiovascular risk. Such findings are consistent with studies of pharmacologically mediated inhibition of CETP in the rabbit, which argue strongly in favor of CETP inhibition as a valid therapeutic approach [Le Goff et al., Pharmacology & Therapeutics 101:17-38 (2004); Okamoto et al., Nature 406:203-207 2000)].
No entirely satisfactory HDL-elevating therapy exists. For example, niacin can significantly increase HDL, but it also has serious toleration issues which reduce compliance. Fibrates and the HMG CoA reductase inhibitors raise HDL-cholesterol only modestly (−10-12%).
Thus, there is a significant unmet medical need for a well tolerated agent which can significantly elevate plasma HDL levels. The net result of CETP activity is a lowering of HDL-C and an increase in LDL-C. This effect on lipoprotein profile is believed to be pro-atherogenic, especially in subjects whose lipid profile constitutes an increased risk for coronary heart disease. By inhibiting CETP activity there is the potential to inverse this relationship towards a lower risk and ultimately to protect against coronary heart diseases and associated mortality.
CETP inhibitors, therefore, are useful as medicaments for the treatment and/or prophylaxis of atherosclerosis, peripheral vascular disease, dyslipidemia, hyperbetalipoproteinemia, hypoalphalipoproteinemia, hypercholesterolemia, hypertriglyceridemia, familial hypercholesterolemia, cardiovascular disorders, angina, ischemia, cardiac ischemia, stroke, myocardial infarction, reperfusion injury, angioplastic restenosis, hypertension, and vascular complications of diabetes, obesity or endotoxemia.
In addition, CETP inhibitors may be used in combination with another compound such as, for example, an HMG-CoA reductase inhibitor, a microsomal triglyceride transfer protein (MTP)/ApoB secretion inhibitor, a PPAR activator, a bile acid reuptake inhibitor, a cholesterol absorption inhibitor, a cholesterol synthesis inhibitor, a fibrate, niacin, an ion-exchange resin, an antioxidant, an ACAT inhibitor or a bile acid sequestrant.